Muammar Gaddafi's regime has "lost all legitimacy" and he must leave power to allow the Libyan people to determine their own future, the international community warned as it boosted support for opposition forces.

After three weeks of Nato-led air strikes, Arab and western ministers meeting in Qatar closed ranks to issue a first unanimous call for Gaddafi to step down, boasting that they were "united and firm in their resolve" about the outcome of the crisis – or, at least, more than they were at the London conference late last month.

But new signs emerged of disagreements over whether UN resolutions allowed the delivery of weapons to the Libyan rebels, with Qatar pushing hard on this highly sensitive issue.

William Hague, the foreign secretary, and Qatar's prime minister, Hamad bin Jassim, chaired a first session of the Libya "contact group" – comprising an unwieldy 21 countries and six international organisations – to explore ways out of the impasse between regime and opposition.

Britain's latest decision – to supply non-lethal body armour to the rebels – was due to be announced by David Cameron before a meeting with Nicolas Sarkozy in Paris. Under the plan 1,000 flak jackets from Ministry of Defence stores will be sent to opposition forces.

Hague, however, sounded ambiguous about whether weapons could legally be supplied. "We understand the resolutions to mean that the arms embargo applies to the whole of Libya," the foreign secretary said. "But in certain circumstances it is possible, consistent with those resolutions, to provide people with the means to defend the civilian population." Other countries, he added, "will interpret the resolution in their own way". Franco Frattini, Italy's foreign minister, went further. "Either we make it possible for these people to defend themselves or we withdraw our claims of support," he said.

Hamad admitted that there were differences of interpretation but added: "Qatar will make things available for the Libyan people to defend themselves."

But Belgium insisted it would not countenance any move to arm the rebels.

Plans for a "temporary financial mechanism" to channel cash to the Benghazi-based opposition were also discussed. Aid to eastern Libya would need to be consistent with UN sanctions, diplomats warned. But the ability to supply basic services would bolster the position and credibility of the Interim National Council. Disagreements surfaced over an Italian call to use frozen Libyan state assets to help the rebels.

Ban Ki-moon, the UN secretary general, highlighted the scale of the crisis when he told delegates that up to 3.6 million Libyans could need humanitarian assistance.

Hague said that Nato's "decisive action" had saved thousands of lives. But there were fresh signs of divisions over the military campaign, with the UK and France, which have conducted the bulk of the attack missions, pressing Italy and Belgium to take part in targeting Libyan forces. "We have sent more ground strike aircraft in order to protect civilians," Hague said. "We do look to other countries to do the same."

The Libyan opposition also urged Nato to do more. "When the Americans were involved the mission was very active and it leant more toward protecting civilians," said spokesman Mahmoud Shammam. Opposition officials later left for the US to lobby the Obama administration.

In response to the Doha statement, Khaled Kaim, Libya's deputy foreign minister, said it was not for other countries "to strip our government of its legitimacy".

Demands by William Hague and his French counterpart Alain Juppe for an intenisfication of Nato air strikes were "a clear call to target and kill civilians and destroy Libyan infrastructure. It has nothing to do with supporting democracy … They are siding with rebels fighting a legitimate government."

Kaim also claimed that militants from Hezbollah and Amal in Lebanon were supporting and training rebels inside Libya. The regime has previously claimed that Al-Qaida was fomenting the uprising.

Anders Fogh Rasmussen, Nato's secretary general, defended the alliance's record after its aircraft flew more than 2,000 sorties. But since its mandate was to protect civilians it had to be cautious. "We do our utmost to strike the right balance," Rasmussen said.

Allied strategy remains a combination of military pressure and hope that Gaddafi will suffer further damaging defections. "The aim is very clear," said France's foreign minister, Alain Juppé. "We must keep up a strong and robust military pressure to convince Gaddafi there is no way out."

International efforts on Libya shift to Cairo on Thursday when the UN's Ban joins the Arab League secretary general Amr Moussa, African Union commission chairman Jean Ping and the EU's foreign policy chief, Lady Ashton. That meeting is expected to discuss a Turkish "roadmap" for peace under which Gaddafi's forces would withdraw from besieged cities such as Misrata. But that would evidently require the agreement of the government in Tripoli.